1. Field of the Invention
The present invention relates to a laminated glass structure, more particularly, relates to a laminated glass structure suppressing turbidity arising along with a lapse of time. Laminated glass assemblies have been widely used for windows and sun roofs for automobiles, windows for airplanes, ships and buildings and so on as so-called safety glass because pieces of glass do not scatter at the time of the breakage of a glass sheet and the penetration resistance is high. At present, the laminated glass assemblies have been widely used for a wind shield glass for automobiles from the viewpoint of assuring safety. There has been also proposed a type of laminated glass of which the bonding surface side is coated with a transparent conductive film so that the laminated glass has both defogging function and solar radiation reflecting function. As the transparent conductive film, a single-layered metal film such as an Au film or an Ag film, a single-layered metal oxide film such as an ITO film or a SnO.sub.2 film or a multi-layered film wherein an Ag film is interposed between dielectric films of metal oxide such as ITO (Indium-Tin-Oxide), TiOx, SnOx, ZnOx have been used. Since the single-layered metal film and the single-layered metal oxide film have drawbacks in color tone, durability and electric resistance, the multi-layered film wherein the Ag film is interposed between the metal oxide films of dielectric substances such as ZnO has been widely used.
2. Discussion of Background
FIG. 3 shows an example of a conventional laminated glass structure in which a transparent conductive film is formed by a multi-layered film having an Ag film between dielectric films in order to give a defogging function and a solar radiation reflecting function.
The above-mentioned laminated glass has a plastic interlayer 13 made of polyvinyl butyral (PVB) at the bonding surface between a glass sheet 11 arranged at the exterior side of a vehicle and a glass sheet 12 arranged at the interior side, and an Ag film 16 is interposed between dielectric films 15, 17 such as ZnOx films as a dielectric substance which are arranged between the glass sheet 11 at the exterior side of the vehicle and the plastic interlayer 13, whereby a transparent conductive film 14 consisting of three-layered films is interposed between the glass sheet 11 and the plastic interlayer 13 so as to perform the both functions of defogging and solar radiation reflecting. The dielectric films 15, 17 are to increase visible light transmittance by an optical interference effect with the metal film 16.
As the plastic interlayer 13, PVB (polyvinyl butyral), EVA (ethylene-vinyl acetate copolymer), urethane or the like may be used. Especially, the PVB has been generally used as laminated glass assemblies for vehicles which require especially safety because it has excellent penetration resistance, and is chemically and optically stable for a long period of time. In this case, a PVB film containing a predetermined amount of moisture is used in order to provide excellent penetration resistance.
In the conventional laminated glass structure as shown in FIG. 3, it is possible to impart a defogging function by heating the transparent conductive film 14 arranged at the bonding surface by supplying an electric current. Further, since the transparent conductive film 14 possesses a solar radiation reflecting function itself, a cooling load of air-condition can be reduced, so that it effectively functions to save energy.
However, it was found that a phenomenon of turbidity has partially occurred upon expiration of a long period of time in a case that a laminated glass is formed by arranging the above-mentioned transparent conductive film 14 consisting of a multi-layered film including therein the Ag film 16 between the dielectric films 15, 17 made of a metal oxide.